Method of processing oil refining waste

ABSTRACT

The present invention relates to a method of processing oil refining waste, the method comprising feeding the waste into a vessel and heating the waste such that it liberates volatile hydrocarbons, wherein the waste is heated using far infrared radiation, and wherein the liberated volatile hydrocarbons are collected for subsequent use.

FIELD OF THE INVENTION

The present invention relates to a method of processing oil refining waste, and in particular to a method of processing such waste so as to recover usable hydrocarbon products therefrom. The invention also relates to hydrocarbon products produced in accordance with the method.

BACKGROUND OF THE INVENTION

The refining of crude oil and petroleum inherently generates a significant amount of oil refining waste. As used herein, the expression “oil refining waste” is intended to mean collectively the residuals of any crude oil and petroleum acquisition, transporting, storing, and refining operation, and includes, but is not limited to sludges, bottoms, waxes, oils, greases, media contaminated with such waste such as contaminated filter media and soils, and any combination thereof.

Depending upon the source of crude oil, feed stock delivered to a given refinery may contain various non-refinable components such as high molecular weight organic compounds, silt/sand/soil, salt, sulphur, metals and their salts, water and ash. Such components can settle to the bottom of storage tanks and become so highly bound to and/or emulsified with refinable hydrocarbons as to resist conventional separation by processes such as filtration and centrifugation. Typical tank bottom sludge can contain as much as 30-45% by weight water and 5-20% non-refinable solids and is not considered suitable for refining. Inevitably the sludge must be removed from the tanks and disposed of in an appropriate manner.

Similarly, when oil feed stocks are refined using conventional cracking and fractionating equipment, high molecular weight organic compounds and various non-volatile/crackable components are condensed or trapped in the cracker or still bottoms. As with the sludges, the bottoms are not considered suitable for further refining and need to be disposed of in an appropriate manner.

Until quite recently oil refining waste was disposed of in landfill. However, disposal regulations have become more stringent and the cost of processing oil refining waste to render it safe for disposal has escalated. Both of these trends may be expected to continue in the future.

A number of methods for processing oil refining waste to render it more suitable for disposal are known. One such method involves processing the waste by pyrolysis. This typically involves introducing the waste into a vessel (also known as pyrolysis reactor) and heating the vessel, for example using gas burners, so as to heat the waste contained within the vessel to temperatures that promote pyrolysis and liberation of volatile hydrocarbon products therefrom. The liberated volatile hydrocarbon products can be collected and further refined if required to afford useful petroleum products such as diesel fuel.

However, conventional pyrolysis techniques for processing oil refining waste are renowned for being energy inefficient. In particular, the heated vessels are prone to significant radiant heat losses, and a thick insulating layer of carbonaceous char or pyrolytic residue typically builds up on the inner heat exchanging surfaces of the pyrolysis vessel (a problem commonly referred to as “coking”). Coking reduces thermal transfer from the vessel to the waste and necessitates frequent stoppages in the process to enable the vessel to be de-coked. Conventional techniques also generally lack the ability for precise and uniform heating of the waste, which can adversely impact on the conversion efficiency of waste into useful volatile hydrocarbon products. Such process limitations adversely impact on the commercial viability of the technology.

An opportunity therefore remains to address or ameliorate one or more disadvantages or shortcomings associated with existing methods of processing oil refining waste, or to least provide a useful alternative.

SUMMARY OF THE INVENTION

The present invention therefore provides a method of processing oil refining waste, the method comprising feeding the waste into a vessel and heating the waste such that it liberates volatile hydrocarbons, wherein the waste is heated using far infrared radiation, and wherein the liberated volatile hydrocarbons are collected for subsequent use.

By the method of the invention, oil refining waste is heated using far infrared radiation (FIR) so as to liberate volatile hydrocarbons from the waste and leave behind non-volatile residues. The volatile hydrocarbons are collected (and if required further refined) to provide useful petroleum products such as diesel, gasoline and liquid petroleum gas (LPG). The non-volatile residues left behind are advantageously relatively inert and non-toxic and can be used as, for example, a bituminous additive in road making or simply disposed of in landfill.

The method of the invention can advantageously be conducted in an effective and efficient manner. This is believed to be at least in part due to using FIR to heat the waste. In particular, it has been found that the waste can be heated significantly faster and the temperature of the waste controlled more readily by using FIR compared with using conventional heating means. The waste can also be heated in uniform manner, thereby minimising if not avoiding altogether the formation of hotspots. Furthermore, FIR heating has been found to not only minimise radiant heat loss during processing but also reduce the amount of coke deposition within the vessel. These processing advantages collectively enhance the efficiency of being able to recover value added products from the waste.

Further aspects of the invention are discussed in more detail below.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Preferred embodiments of the invention will herein be illustrated by way of example only with reference to the accompanying drawing in which:

FIG. 1 shows a process flow diagram of an apparatus that maybe used to perform the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

The method according to the invention involves processing oil refining waste. For avoidance of any doubt, the expression “oil refining waste” used in the context of the invention is intended to have the same meaning as hereinbefore defined. Thus, the waste can be the residuals of any crude oil and petroleum acquisition, transporting, storing, and refining operation, and includes, but is not limited to sludges, bottoms, waxes, oils, greases, media contaminated with such waste such as contaminated filter media and soils, and any combination thereof. Those skilled in the art will appreciate that such waste is generally not considered suitable for refining by conventional means.

The method in accordance with the invention is particularly robust in terms of the composition of feedstock waste used therein. For example, the oil refining waste may contain non-hydrocarbon products such as silt/sand/soil, salt, sulphur, metals and their salts, water, catalyst residues and ash.

The method comprises feeding the oil refining waste into a vessel. The waste may be fed into the vessel by any suitable means, for example by extrusion or pumping. The means by which the waste is fed into the vessel will of course be designed with the physical and chemical properties of the waste in mind. If necessary, the waste can be preheated so as to facilitate feeding it into the vessel.

The method may be performed in a continuous, semi-continuous or batch mode. The means by which the oil refining waste is fed into the vessel will of course be adapted to suit the particular mode of operation. Given that the volumes of oil refining waste to be processed can be quite large, it may be preferable to operate the method in a continuous mode.

There is no particular limitation on the type of vessel that may be used in accordance with the invention provided it can readily contain the waste and withstand the temperatures employed. The vessel may, for example, be made from stainless steel. Those skilled in the art may commonly refer to the vessel as a “pyrolysis reactor”.

The vessel will also be adapted so as to allow the volatile hydrocarbons liberated from the waste to be collected. For example, the vessel will generally have at least one outlet positioned in the head space above the oil refining waste designed to allow for the collection of the volatile hydrocarbons. The volatile hydrocarbons collected will typically be a mixture of compounds such as olefins, paraffins, and aromatics. The volatile hydrocarbons may, for example, comprise a mixture of C₁-C₂₂ hydrocarbon compounds. Those skilled in the art will appreciate that such compounds may be readily used in numerous petroleum products.

In addition to being adapted to collect the volatile hydrocarbons, the vessel may also be adapted to allow removal of the non-volatile residues left behind. In that case, there will generally also be at least one outlet in the vessel designed to remove such residues.

The vessel may also be fitted with a means for agitating or stirring the oil refining waste within the vessel so as to promote even heating of the waste. For example, the vessel may comprise a stirring element which rotates within the vessel and stirs the oil refining waste.

An important feature of the method is that the oil refining waste is heated using FIR such that volatile hydrocarbons are liberated from the waste. Volatile hydrocarbons may be liberated from the waste simply by virtue of thermal desorption of hydrocarbons already present in the waste, and/or by virtue of organic material present in the waste being pyrolysed.

Pyrolysis is a well known chemical process for converting organic materials into volatile hydrocarbons. Pyrolysis may also result in the production of non-hydrocarbon volatiles such as hydrogen gas.

In contrast with conventional pyrolysis techniques, the method of the invention allows the oil refining waste to be pyrolysed at relatively low temperatures (e.g. by heating the waste to temperatures in range of from about 360° C. to about 450° C.). Such low pyrolysis temperatures can be attained due to the efficient and effective transfer of heat from the FIR to the oil refining waste.

Pyrolysis of the oil refining waste will generally be conducted in the absence of oxygen, and may be conducted in the presence of a suitable catalyst to promote thermal cracking of the hydrocarbon constituents in the waste.

The ability to rapidly heat and control the temperature of the waste using FIR, and then conduct pyrolysis at relatively low temperatures, has been found to improve the efficiency of converting the waste into volatile hydrocarbons and also reduce the formation of coke within the vessel. Without wishing to be limited by theory, it is believed that relatively low temperatures and short exposure time to such temperatures maximises the formation of volatile hydrocarbons and also reduce the formation of coke within the vessel.

Heating of the oil refining waste by FIR may be conducted by any suitable means. For example, one or more FIR heaters may be located within the vessel. Generally, a plurality of FIR heaters will be positioned within the vessel. At lease part in not all of the one or more FIR heaters will be in contact with the waste. The FIR heaters therefore provide an “internal” or “direct” means for heating the waste, this being in contrast with the “external” or “indirect” means used in conventional pyrolysis techniques.

Those skilled in the art will appreciate that FIR defines the part of the electromagnetic spectrum that falls in between middle infrared radiation and microwave radiation.

Conventional FIR heaters can advantageously be used in accordance with the invention to provide the source of FIR. The FIR heaters will of course be configured to withstand conditions encountered by the method. For example, the FIR heaters may be in the form of ceramic rod elements sheathed with stainless steel sleeves coated with an appropriate emitter compound. The FIR heaters can be positioned with the vessel so as to be partly or fully immersed in the refining oil waste and promote efficient and effective heating thereof.

The volatile hydrocarbons liberated from the oil refining waste may be collected by any suitable means such as a condenser. Generally, the vessel will be adapted to comprise a reflux column fractionator such that the collected volatile hydrocarbons can be separated according to their boiling point. If desired, lower boiling point fractions (i.e. “lighter” fractions) may be introduced at the top of the column so as to strip by counter current absorption higher boiling point fractions (i.e. “heavy” fractions) from the hydrocarbon vapour rising up the packing inside the column. In this way, higher boiling point fractions may be returned to the reactor to be subjected to a further pyrolysis.

The collected hydrocarbons may be then be used in various applications/products or, if desired, one or more of these hydrocarbon fractions may be subjected to refining in a second reflux column fractionator which may be used to further separate the fractions into specific petroleum products such as diesel and gasoline.

The method of the invention will also generally yield a proportion of non-condensable (at atmospheric pressure) hydrocarbons such as light hydrocarbons in the LPG range. Such hydrocarbon gas can be disposed of by flaring. Alternatively, it may be used to fuel a power generation unit that can generate electricity for powering equipment associated with performing the method of the invention. For example, the generated electricity may be used to power the FIR heaters and other heating and pumping units be used in the method.

In addition to liberating volatile hydrocarbons, heating of the oil refining waste will also generate non-volatile residues. These residues will typically be in the form of carbonaceous residues, and together with any other non-volatile material present, will for convenience hereinafter be referred to as “pyrolytic residues”. The vessel may be adapted to readily remove or discharge the pyrolytic residues by, for example, an outlet valve located at the bottom of the vessel. The pyrolytic residues may be discharged from the vessel together with at least some unprocessed oil refining waste. In that case, the discharged mixture may be subjected to a second heating process, for example by being past through a heat tunnel. Heating of the discharged mixture in the tunnel may be promoted by any suitable means. For example, heating may be promoted by subjecting the residues to FIR and/or microwave radiation. The pyrolytic residues will generally be a good microwave receptor and heating by this means is particularly effective.

Upon heating the discharged mixture in the heat tunnel any volatile hydrocarbons present are volatilised from the mixture to yield a free flowing friable powder. The volatilised hydrocarbons may be reintroduced to the vessel to be processed according to the method or collected for subsequent use by means herein described.

The now isolated pyrolytic residues can advantageously be used as, for example, a bituminous additive in road making or simply disposed of in landfill.

Pyrolytic residues formed by the method of the invention have been found to be relatively inert and non-toxic. Without wishing to be limited by theory, it is believed any toxic materials such as heavy metals within the residues become strongly bound within a vitreous carbonaceous matrix. The vitreous carbonaceous matrix itself is relatively inert and bound toxic materials within it are not readily separated therefrom, for example by acid leaching. The pyrolytic residues are therefore considerably safer for use in a given application or to be disposed in landfill.

The oil refining waste can also advantageously be processed according to the invention in admixture with other hydrocarbon based materials. For example, the method may further comprise feeding into the vessel hydrocarbon based products such as plastic and paint.

The method in accordance with the invention is particularly robust and there is no particular limitation regarding the type of other hydrocarbon based products that may be introduced to the vessel. For example, the hydrocarbon based products may comprise plastics and/or waste alkyd paint. The plastic material will typically be waste plastic and may be a mixture of different plastics.

The method of the invention is particularly suited for processing waste plastic that would otherwise prove difficult to recycle. Such plastic materials include, but are not limited to soiled plastics such as agricultural plastics, mulch/silage/green house films and dripper/irrigation tube, and plastic laminates, coextrusions and multilayer packaging films, particularly those with printing and aluminium foil layers.

Suitable plastic materials that may be processed according to the method of the invention, include, but are not limited to, polyolefines such as polyethylene and polypropylene, polyesters such as polyalkyleneterephthaltes, polyamides such as nylons, polystyrene and polyvinylchloride.

Performing the method of the invention using a combination of oil refining waste and plastic material has been found to advantageously give higher yields of the volatile hydrocarbons and lower yields of pyrolytic residues.

Where an additional hydrocarbon based product is also fed into the vessel, it maybe combined with the oil refining waste and fed as a single stream into the vessel, or simply fed into the vessel in a separate stream either concurrently or sequentially relative to the oil refining waste.

The method according to the present invention is preferably conducted using an apparatus schematically represented in the flow diagram shown in FIG. 1. In that case, oil refining waste and if present other hydrocarbon based products (hereinafter simply referred to as the feedstock) may be conveyed by a feeding means (10) such as an extruder or centrifugal pump into the vessel (20). The vessel comprises a mixing element (30) such as an impellor stirrer for agitating the feedstock contained therein. Generally, the oil refining waste will provide adequate liquidity to enable stirring. However, in some cases it may be necessary to heat the feedstock to achieve the required state of liquidity. The feedstock will generally be agitated so as to maintain any solids present therein in suspension.

In accordance with the method, the feedstock is heated by FIR. Located within the vessel (20) is therefore a far infrared radiation (FIR) emitter (40). The FIR emitter (40) will typically be in the form of a plurality of FIR heaters. The FIR heaters may comprise ceramic rods sheathed with stainless steel sleaves coated with an appropriate emitter compound. Each FIR heating rod will generally have a minimum heating capacity of 12 kW. The feedstock will generally be heated to a temperature ranging from about 360° C. to about 450° C. Heating of the feedstock will promote liberation of volatile hydrocarbons contained therein and also volatile hydrocarbons formed by pyrolysis. The liberated hydrocarbons may be collected using condenser (50) such as a reflux column fractionator. One or more of the collected hydrocarbon fractions may be passed into a second condenser (60) such as reflux column fractionator and heated by a heating means (70) such as a FIR emitter to promote further fractionation of the collected volatile hydrocarbons. This further fractionation may, for example, enable the volatile hydrocarbons to be separated into petroleum products such as gasoline (80) and diesel (90). The volatile hydrocarbons collected may also comprise non-condensable (at atmospheric pressure) hydrocarbons such as hydrocarbons in the LPG range. Such hydrocarbons may be disposed of by a flaring (not shown) or used to fuel a power generation unit (100). This power generation unit may be used to power the FIR heaters (emitters) and electric motors associated with equipment used in the process.

The vessel will generally be adapted to enable removal of residue therefrom. For example, the vessel may comprise a valve or an outlet port (110) for removing or discharging oil refining waste that has been subjected to FIR heating, generally in the form of pyrolytic residues. On removing the residues, some unprocessed feedstock may also be removed. In that case, the feedstock/residue mixture may be discharged into a heat tunnel (120) in which a heating means (130) such as a FIR and/or microwave heater (emitter) may be used to heat the feedstock/residue mixture and drive off volatile hydrocarbons. Any volatile hydrocarbons formed may be reintroduced to the vessel or collected (not shown) using the condenser (50). Upon being subjected to this further heating process, a residue in the form of a friable powder (140) is produced.

Such a system may be operated in continuous, semicontinuous and batch modes. The system may also be operated substantially closed thereby minimising any emission to the atmosphere.

Accordingly, there is also provided an apparatus for processing oil refining waste, the apparatus comprising: (1) a vessel to contain the oil refining waste, (2) a far infrared radiation (FIR) emitter located within the vessel for heating the oil refining waste such that it liberates volatile hydrocarbons, and (3) a condenser for collecting the liberated hydrocarbons.

There is further provided an apparatus when used for processing oil refining waste, the apparatus comprising: (1) a vessel to contain the oil refining waste, (2) a far infrared radiation (FIR) emitter located within the vessel for heating the oil refining waste such that it liberates volatile hydrocarbons, and (3) a condenser for collecting the liberated hydrocarbons.

The apparatus may comprise one or more of the following features: a feeding means, such as an extruder or centrifugal pump, for conveying the oil refining waste, and if present other hydrocarbon based products, into the vessel; the vessel may comprise a mixing element such as an impellor stirrer for agitating the oil refining waste, and if present other hydrocarbon based products, contained therein; the FIR emitter may be in the form of a plurality of FIR heaters; the FIR heaters may be in the form of ceramic rods sheathed with stainless steel sleaves coated with an emitter compound; each FIR heating rod may have a minimum heating capacity of about 12 kW; the condenser may be in the form of a reflux column fractionator; a second reflux column fractionator may be coupled to the first to promote further fractionation of the collected volatile hydrocarbons; an electricity generator powered by liberated hydrocarbon such as LPG; the vessel may comprise a valve or an outlet port for removing or discharging residue from the oil refining waste that has been subjected to FIR heating; a heat tunnel into which the residue is discharged and subjected to heating means, such as a FIR and/or microwave heater (emitter), to drive off volatile hydrocarbons from the residue; and a means for transporting volatile hydrocarbons driven off the residue to (a) the condenser for collection, or (b) the vessel for further processing.

Embodiments of the invention are further described with reference to the following non-limiting examples.

EXAMPLES Comparative Example 1

A thick hydrocarbon oil sludge collected from tank bottoms was fed into the pyrolysis process via a monopump. The oil sludge was highly viscous. The oil sludge comprised about 45-55 wt % oil, 25 wt % inert solids and 20-25 wt % water. The tank bottoms were pyrolyzed in a stainless steel (SS316) pyrolysis vessel heated indirectly via gas burners (‘outer heating’). After 48 hrs a 50 mm layer of carbonization had deposited inside the pyrolysis chamber and the efficiency of heating had decreased by 40% due to the insulating layer of carbon that had formed on the heat exchanging surface.

Example 1

A thick hydrocarbon oil sludge collected from tank bottoms was fed into the pyrolysis process via a monopump. The oil sludge was highly viscous. The oil sludge contained about 45-55 wt % oil, 25 wt % inert solids and 20-25 wt % water. The tank bottoms were pyrolyzed in a stainless steel (SS316) pyrolysis vessel heated internally via 43 far infra-red heating rods (‘inner heating’). After 48 hrs only a 2 mm layer of carbonization had deposited on the heating rods and no coking had occurred on the inside of the pyrolysis chamber. There was no measurable reduction in the efficiency of heating.

Example 2

A thick hydrocarbon oil sludge collected from tank bottoms was fed into the pyrolysis process via a monopump. The oil sludge comprised of 45-55 wt % oil, 25 wt % inert solids and 20-25 wt % water. FIR pyrolysis of the 100% tanks bottoms gave 35% mixed oil, 15% non-condensable gas (mainly alkanes less than C₇) and 50% solid carbonaceous residue. The mixed oil was further fractionated into approximately 60% wt. diesel fuel and 40% gasoline.

Example 3

It was found that FIR pyrolysis of 50% tanks bottoms and 50% waste plastics (polyolefins) conducted in a similar manner to Example 1 gave 65% mixed oil, 20% non-condensable gas (mainly alkanes less than C₇) and 15% solid carbonaceous residue.

Co-processing of tank bottoms with waste plastics was found to give yields of mixed oil (diesel and gasoline) and lower yields of residual carbonaceous residues.

Properties of diesel produced according to Example 2 is shown in Table 1 below.

TABLE 1 Property Diesel Test Results Flash Point 66 deg. C. Cetane index 57 Water 0.02 Sulphur 24 ppm Cold filter plugging point −18 deg. C.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. 

1. A method of processing oil refining waste, the method comprising feeding the waste into a vessel and heating the waste such that it liberates volatile hydrocarbons, wherein the waste is heated using far infrared radiation, and wherein the liberated volatile hydrocarbons are collected for subsequent use.
 2. The method according to claim 1 further comprising feeding into the vessel plastic material.
 3. The method according to claim 1, wherein the far infrared radiation is provided by a plurality of far infrared radiation heaters that are each at least in part immersed within the waste.
 4. The method according to claim 3, wherein the far infrared heaters are in the form of ceramic rod elements sheathed with stainless steel sleaves that are coated with an emitter compound.
 5. The method according to claim 1, wherein the waste is heated to a temperature ranging from about 360° C. to about 450° C.
 6. The method according to claims 1, wherein the volatile hydrocarbons are collected using a reflux column fractionator.
 7. The method according to claim 1, wherein the collected volatile hydrocarbons comprise at least one of a diesel, gasoline, and liquid petroleum gas (LPG) fraction.
 8. The method according to claim 1 further comprising discharging from the vessel a substantially non-volatile residue formed as a result of heating the waste.
 9. The method according to claim 8, wherein the discharged residue is heated using far infrared radiation or microwave radiation to drive off any residual volatile hydrocarbons.
 10. A hydrocarbon product produced in accordance with the method of claim
 1. 